The following invention relates to implants which are configured to be placed within an intervertebral space between adjacent spinal vertebrae after a disk has been removed from the space and to facilitate fusion of the vertebrae together. More particularly, this invention relates to implants which can be implanted posteriorly in either a minimally invasive or open manner and spread vertebrae adjacent the intervertebral space away from each other to recreate the lumbar lordosis and support the vertebrae while they fuse together.
Spinal fusion procedures are known as an effective treatment for certain spinal conditions. In general, such spinal fusion procedures may involve removal of a disk within an intervertebral space between two adjacent vertebrae. After the disk has been removed an implant can be located within the intervertebral space to push the vertebrae apart. By pushing the vertebrae apart, ligaments and other body structures surrounding the vertebrae are placed in tension and tend, along with the implant, to securely hold the two vertebrae in fixed position relative to each other. It is important to restore as much as possible the height of the intervertebral space. It is also important to restore the angle or xe2x80x9clordosisxe2x80x9d of the intervertebral space. Finally, fusion material is placed within the intervertebral space which induces bone growth within the intervertebral space, effectively fusing the two vertebrae together with the implant typically remaining embedded within this fused vertebra combination.
Placement of the implant within the intervertebral space is accomplished in one of two general ways. First, the intervertebral space can be accessed anteriorly by performing abdominal/thoracic surgery on the patient and accessing the intervertebral space from a front side of the patient. In this anterior procedure major abdominal/thoracic surgery is typically involved. However, the intervertebral space can be generally accessed anteriorly, such that the risk of injury to the nerves is generally reduced and the surgeon has greater flexibility in positioning the implant precisely where desired.
Second, the implant can be inserted posteriorly. Direct posterior access to the intervertebral space requires moving the spinal nerves within the spinal canal towards the midline and can result in nerve injury or scarring. Implantation in the intervertebral space can also be accessed from a location spaced to the left or right side of the spinal column and at an angle extending into the intervertebral space. This approach avoids the spinal canal. A minimally invasive method using small incisions can be used but is must be carefully performed to avoid sensitive spinal structures. Additionally, implants of a smaller size are typically required due to the small amount of clearance between vertebral structures. Hence, the amount of spreading of the vertebrae with a posterior implant is often less than adequate. Additionally, portions of the vertebrae typically need to be at least partially carved away to provide the access necessary to insert the implants posteriorly into the intervertebral space.
Implants for the intervertebral space come in a variety of different configurations, most of which are designed for anterior implantation. One known prior art implant is described in detail in U.S. Pat. No. 5,800,550 to Sertich. The Sertich implant is configured to be implanted posteriorly and comes in two pieces. Two separate incisions are made on either side of the spine and the pieces of the overall implant are inserted generally parallel to each other, but can be angled slightly away from a parallel orientation. The Sertich implant pieces have a rectangular cross section and an elongate form. The pieces are initially implanted with a lesser dimension oriented vertically so that the pieces can easily enter the intervertebral space. The pieces are then rotated 90xc2x0 so that the greater dimension is rotated to vertical, tending to spread the vertebrae vertically to enlarge the intervertebral space.
The implant taught by Sertich is not entirely desirable. Because the Sertich implant involves two entirely separate pieces, they do not stabilize each other in any way and hence provide a less than ideal amount of vertebral stabilization. Additionally, the relatively parallel angle at which they are implanted typically requires removal of portions of the vertebrae and retraction of the spinal nerves to properly implant the pieces of the Sertich implant. If the two pieces of the implant are angled more towards each other, they tend to decrease further in the stability that they provide to the vertebrae. Also, the Sertich implant pieces have a size which requires a relatively large incision to insert into the intervertebral space.
Accordingly, a need exists for a posteriorly placed intervertebral space implant which has a small cross-sectional profile at insertion and yet can provide a large amount of displacement between adjacent vertebrae once placed. The implant must expand sufficiently far apart to restore the height of the intervertebral space and act substantially as a single rigid structure within the intervertebral space after implantation is completed. Such an invention would additionally benefit from being capable of having a greater height in an anterior region such that lordosis can be achieved in an amount desired by the surgeon with an anterior side of the intervertebral space larger than a posterior side of the intervertebral space.
This invention is an intervertebral space implant which is configured to be implanted posteriorly in a minimally invasive or open surgical procedure. The implant includes two separate segments including a primary segment and a secondary segment. The primary segment and the secondary segment enter the intervertebral space through separate incisions on either side of the spine and along paths which intersect within the intervertebral space. To enhance a spreading of the intervertebral space with the implant, the segments have a height between a bottom surface and a top surface which is greater than a lateral width. The segments can thus be introduced into the intervertebral space with the top and bottom surfaces spaced laterally from each other and then be rotated 90xc2x0 so that the top surface is above the bottom surface and a height of the segments is maximized.
Portions of the primary segment and the secondary segment adjacent where the segments intersect are removed to allow the segments to lie in a substantially common plane. Preferably, the primary segment includes a tunnel passing laterally through the primary segment near a midpoint thereof. The secondary segment is provided with a neck near a midpoint thereof which has a lesser height than other portions of the secondary segment. The tunnel is sized so that the secondary segment can pass through the tunnel in the primary segment and then be rotated with the neck of the secondary segment within the tunnel of the primary segment.
After the secondary segment has been rotated the two segments are interlocking together in a crossing pattern forming the implant assembly of this invention. Hence, the implant assembly of this invention provides the advantage of having a relatively low profile for insertion posteriorly in a minimally invasive manner and yet results in an overall implant assembly which has separate segments interlocking together to form a single substantially rigid implant assembly to maximize stabilization of the vertebrae adjacent the intervertebral space.
Additionally, the segments are formed in a manner which facilitates height expansion of the segments after implantation, especially at distal ends of the segments. Such additional height expansion further stabilizes vertebrae adjacent the intervertebral space and provides lordosis to the intervertebral space.
Specifically, the primary segment is preferably formed with a top structure separate from a bottom structure which pivot relative to each other, such as about a hinge. A passage passes between the top structure and the bottom structure. A shim can pass along the passage and cause a distal end of the primary segment to be expanded in height when the shim enters a tapering end portion of the passage. The distal end of the primary segment is thus expanded in height to an extent desired by a surgeon to provide a desirable amount of xe2x80x9clordosisxe2x80x9d for the spinal fusion procedure.
Similarly, the secondary segment is preferably formed from a top jaw and a bottom jaw which can pivot relative to each other, such as about a hinge. A bore passes between the top jaw and the bottom jaw and a wedge is caused to move within the bore in a manner causing the top jaw and the bottom jaw to be spaced apart and causing a height of the secondary segment to be increased at a first distal end of the secondary segment.
The insertion of the segments themselves as well as the movement of shims and wedges within the segments to enhance their height is all accomplished through a small posterior incision. A variety of different hinge arrangements, shim and wedge arrangements and other structural variations are provided for the segments of the implant assembly.
Accordingly, a primary object of the present invention is to provide an implant for an intervertebral space which can be implanted posteriorly and still provide a substantially rigid implant assembly for spreading and stabilization of the vertebrae adjacent the intervertebral space.
Another object of the present invention is to provide an implant assembly having separate segments which are as low profile as possible so that posterior implantation can be accomplished in as minimally invasive a surgical procedure as possible.
Another object of the present invention is to provide an implant assembly for an intervertebral space which is initially entered into the intervertebral space in separate segments which are later interlocked together.
Another object of the present invention is to provide an intervertebral space implant assembly which can be adjusted in height to maximize a size of the intervertebral space generally and to allow for selective height adjustment within different portions of the intervertebral space, to provide a surgeon with a maximum amount of flexibility in positioning vertebrae adjacent the intervertebral space as precisely as desired.
Another object of the present invention is to provide an implant assembly which can be located within an intervertebral space with little risk of damage to sensitive surrounding tissues.
Other further objects of the present invention will become apparent from a careful reading of the included drawing figures, the claims and detailed description of the invention.